Dispersion strengthening is a well-known strengthening method for metallic materials, in which dispersed particles consisting of carbide, nitride, or oxide of a metal are dispersed in another metal matrix, by which the mechanical properties of matrix metal are improved by the function of dispersed particles.
Oxide-dispersed alloys to which a metallic oxide is applied as dispersed particles have many kinds, and are in widespread use. For example, an alloy in which the oxide particles of a metal such as zirconium are dispersed in platinum, which is a matrix metal, is called strengthened platinum, and is used as a material in a high-temperature region, for example, as a construction material for a glass manufacturing apparatus because of its improved high-temperature creep strength.
Many manufacturing methods for an oxide-dispersed alloy are basically based on powder metallurgy. Generally, alloy powder in a state in which the oxide of additive metal is dispersed in a matrix metal is manufactured, and the alloy powder is moldedly solidified, for example, by sintering, and is further worked as necessary. As a method of introducing an oxide to manufacture alloy powder in which dispersed particles are dispersed in a matrix metal, several methods are available.
As a means for introducing the oxide of additive metal into a matrix metal, there is available a method in which matrix metal powder and powder of additive metal oxide are introduced into a high-energy ball mill such as attritor and are agitated to mechanically alloy the matrix metal and the oxide (mechanical alloying), by which alloy powder in which an oxide is dispersed in a matrix metal is formed.
Also, as another method of introducing an oxide, powder consisting of an alloy (solid solution) of a matrix metal and an additive metal is first manufactured, thus manufactured powder is heated at a high temperature in an oxidizing atmosphere, and the additive metal in the alloy is oxidized (internal oxidation), by which powder in which an oxide is dispersed in the matrix metal can be manufactured. In the case of the above-described strengthened platinum, alloy powder is often manufactured by this internal oxidation method. For example, Patent Document 1 disclosed by the applicant of this invention discloses a manufacturing method for strengthened platinum, in which internal oxidation processing and wet grinding processing are combined.
Patent Document 1: Japanese Patent Application Laid-Open No. 8-134511
For the dispersion strengthened alloy, in order to sufficiently demonstrate the strengthening mechanism while properties other than strength are not impaired, it is important to control the quantity of dispersed particles and the dispersion state. An alloy in which the quantity of dispersed particles is at a necessary minimum, and fine dispersed particles are dispersed uniformly in a state of high dispersion is an ideal alloy. For example, if oxide particles are increased beyond necessity, not only the properties such as weldability are degraded but also the strength properties are sometimes affected adversely.
In the above-described methods, an ideal dispersion state cannot necessarily be realized. In the method in which a matrix metal and the oxide of additive metal are mixed mechanically, the oxide is not always dispersed uniformly because the mixing is basically mixing of a solid and a solid. Also, it is necessary to manufacture powder of additive metal oxide, but this manufacture itself is difficult to do.
On the other hand, in the method in which alloy powder is internally oxidized, an oxide can be dispersed uniformly by oxidizing a uniform solid solution, which is an advantage. However, because of processing performed in a high-temperature atmosphere, there is a fear of growth of the yielded oxide. Also, in the method using internal oxidation, oxygen diffusion occurs preferentially at the grain boundary at the time of oxidation, and the additive metal diffuses to the grain boundary to yield an oxide, so that an ideal degree of dispersion cannot sometimes be obtained. Further, crystal grain growth of a matrix metal phase is liable to take place, and the grain boundary area decreases, so that the degree of dispersion of dispersed particles at the time of internal oxidation tends to decrease easily. Therefore, an alloy having a high strength is not always obtained finally.
The present invention has been made based on the above background, and accordingly an object thereof is to provide a manufacturing method for an oxide dispersed alloy by which an alloy can be manufactured in which oxide particles are dispersed in an ideal state.